Chapter 50. Writing
A Foreign Data Wrapper

All operations on a foreign table are handled through its
foreign data wrapper, which consists of a set of functions that
the planner and executor call. The foreign data wrapper is
responsible for fetching data from the remote data source and
returning it to the PostgreSQL
executor. This chapter outlines how to write a new foreign data
wrapper.

The foreign data wrappers included in the standard
distribution are good references when trying to write your own.
Look into the contrib/file_fdw
subdirectory of the source tree. The CREATE FOREIGN DATA
WRAPPER reference page also has some useful details.

Note: The SQL standard specifies an interface for
writing foreign data wrappers. However, PostgreSQL does not
implement that API, because the effort to accommodate it into
PostgreSQL would be large, and the standard API hasn't gained
wide adoption anyway.